This application claims the priority of German Patent Document 100 05 387.4, filed Feb. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus of a spinning machine for the drafting and subsequent condensing of a fiber strand, comprising a condensing zone located downstream of a front roller pair of a drafting unit, an air-permeable transport belt which transports the fiber strand through the condensing zone, a suction channel arranged at the condensing zone, which suction channel guides the transport belt onto a sliding surface, a suction slit arranged in the sliding surface, a nipping roller which presses the fiber strand and the transport belt to the sliding surface at the end of the condensing zone, a top weighting arm of the drafting unit, which top weighting arm supports the nipping roller and a front pressure roller of the front roller pair, and weighting structure for the front pressure roller and the nipping roller.
Important for the condensing of a fiber strand leaving a drafting unit is that the fiber strand is transported in the condensing zone disposed on an air-permeable transport element and still in a twist-free state and having essentially fibers which lie parallel to one another, and that in the condensing zone an air stream is generated which flows through the transport element, which air stream determines or assists the degree of condensing depending on its width and/or direction and which assists positioning of the fibers transversely to the transport direction so that the fiber strand is bundled or condensed. In the case of a fiber strand condensed in this way, a spinning triangle does not occur, so that the arising thread is more even, tear resistant and less hairy.
An apparatus of the above mentioned type is disclosed in U.S. Pat. No. 6,108,873. In this known apparatus, the front pressure roller and the nipping roller are arranged at a joint rocker, which in turn can be swivelled around a swivel axle. The rocker is held by means of a loading spring, which in turn is arranged in the top weighting arm of the drafting unit. Due to the position of the swivel axle, and thus by means of the choice of lever lengths extending to the front pressure roller and to the nipping roller, the pressure forces of the front pressure roller and the nipping roller can be distributed in the desired ratio.
In practice it has been shown that this system presents problems due to the great differences between the two pressure forces. It is an object of the present invention to avoid this disadvantage of the above mentioned apparatus and to create an apparatus which is more flexible in relation to the loading pressures.
This object has been achieved in accordance with the present invention in that the weighting structure comprises a pressure spring each for the front pressure roller and for the nipping roller.
By this arrangement, the front pressure roller and the nipping roller can be varied and adapted to the required nipping pressures, whereby the fact that the pressure of the front pressure roller is very high due to the high drafting forces and the pressure of the nipping roller, which practically no longer effects a draft, is relatively low, should be taken into consideration. A rocker for the apparatus need not hereby be omitted, which rocker could permit, for example, that the nipping roller is arranged at a holding device, which can be swivelled around a swivel axle, which is disposed coaxially to the axle of the front pressure roller.
In certain preferred embodiments of the invention, the nipping roller can drive the transport belt and in turn be driven by the front roller pair.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.